Hybrid optical element and photodetector device

ABSTRACT

The present invention concerns a hybrid optical element including at least one optical element ( 2 ) attached to one surface of a substrate ( 1 ), a semiconductor laser ( 3 ) and a photodetector ( 4 ) attached to the other surface of the substrate ( 1 ) and an intermediate member (relay substrate) ( 5 ) interposed between the substrate ( 1 ) and the photodetector ( 4 ). The intermediate member ( 5 ) has a through hole ( 6 ) through which a light flux incident on the photodetector ( 4 ) is allowed to pass and a part with a conductivity by which a terminals of the photodetector ( 4 ) are connected to a conductor pattern on the substrate ( 1 ).

TECHNICAL FIELD

[0001] The present invention relates to a hybrid optical element andphotodetector device employed for an optical pick-up device that writesan information signal in an optical recording medium such as an opticaldisc or reads out the information signal recorded on the opticalrecording medium.

BACKGROUND ART

[0002] In a recording and reproducing system which employs, as arecording medium, an optical disc such as a CD (Compact Disc), what iscalled an MD which is a small magneto-optical disc with a diameter of 64mm, a DVD (Digital Versatile Disc) or the like, a device has beenhitherto demanded to be more compact, lighter and more inexpensive. Inorder to meet such a demand, individual component parts need to becompact and light and inexpensively manufactured. An optical pick-updevice for the above-described optical disc realizes a compact, lightand further inexpensive structure of the device itself by integrating asemiconductor laser serving as a light source and a photodetector suchas a Pin diode composed of silicon (Si) as a base material.

[0003] The photodetector used for the optical pick-up device is formedas what is called a “PDIC” (photodetector device) composed of one chipin which is incorporated an integrated circuit for performing processesand calculation of a light receiving signal such as receiving lightreflected from the optical disc, converting the light into an electricsignal and outputting the signal to integrate functions for receivinglight, calculating the received light, converting the received lightinto an electric signal and outputting the electric signal, so that thecompact, light and further inexpensive optical pick-up device using thephotodetector is realized.

[0004] Here, are generally called a hybrid optical element, elementscapable of being integrated and compact by adding optical parts such asa prism, a lens, a diffraction grating, a hologram, etc. to the lightsource and the photodetector forming the optical pick-up device. Asshown in FIG. 1, the hybrid optical element includes a semiconductorlaser 101, a PDIC 102 and optical elements such as lenses, prisms,diffraction gratings, holograms, etc. arranged on a substrate 104 whichare electrically or mechanically connected together.

[0005] The semiconductor laser 101 is attached to a sub-mount 101 a by achip mount step. The sub-mount 101 a is attached to the PDIC 102 by adie bonding step. At this time, in the sub-mount 101 a, connectionterminals are electrically connected to wiring pads of a PDIC substrate102 a forming the PDIC 102. On the PDIC substrate 102 a, markers 102 cshowing positions in which the sub-mounts 101 a are arranged areprovided. The sub-mount 101 a has its attached positions positioned tothe PDIC substrate 102 a and is attached to the PDIC substrate 102 a insuch a manner that markers 101 b provided on the sub-mount 101 a itselfare made to correspond to the markers 102 c.

[0006] To the PDIC substrate 102 a of the PDIC 102, photodetectors 102 bare attached. On the PDIC 102, a prism 103 is attached by a prism mountstep. The PDIC 102 is attached on a substrate 104 by a PDIC mount step.

[0007] In manufacturing the hybrid optical element, markers 104 a as themarks of positions are further previously provided on the substrate 104and the respective parts are attached to the substrate 104 by usingthese markers 104 a as references for positioning. The above-describedpositioning method is referred to as a “passive alignment”. The accuracyof the hybrid optical element is determined by the accuracy of apositioning (alignment) step of each parts relative to the substrate.

[0008] In the substrate 104, electrodes 104 b to which the PDIC 102 iselectrically connected are provided. The PDIC 102 is electricallyconnected to the electrodes 104 b by a wire bonding step as shown byarrows in FIG. 1.

[0009] The parts respectively forming the hybrid optical element arebasically arranged as shown in FIG. 2. That is, the semiconductor laser(light source) 101, a signal recording surface of an optical disc 107and a light receiving part of the photodetector 102 b are respectivelyarranged to be located at positions of image points through thereflection surface of the prism 103. The positions of the respectiveparts are arranged so as to deviate from other positions.

[0010] In other words, a light flux outgoing from the semiconductorlaser 101 is a diffusion light flux that is light having only asemiconductor laser side as a focal point. The light flux outgoing fromthe semiconductor laser 101 is allowed to be a parallel light flux by acollimator lens 105 and converged on the signal recording surface of theoptical disc 107 by an objective lens 106. At this time, the objectivelens 106 is controlled to move in a focusing direction parallel to anoptical axis so that a focal point is always formed on the signalrecording surface of the optical disc 107.

[0011] The light applied to the signal recording surface of the opticaldisc 107 is reflected on the signal recording surface and converged onlenses 108 and 109 through the objective lens 106, the collimator lens105 and the prism 103 and returned to the photodetector 102 b. Theoptical elements are respectively arranged so that the reflected lightfrom the signal recording surface of the optical disc 107 focuses on thelight receiving part of the photodetector 102 b. That is, the light islocated respectively at the focal points in the semiconductor laser 101,the signal recording surface of the optical disc 107 and the lightreceiving part of the photodetector 102 b. This means that the lightsource, the signal recording surface and the light receiving part arelocated at the positions of image points.

[0012] On the other hand, for more inexpensively providing the hybridoptical element, the number of parts is devised to decrease as many aspossible. For instance, as shown in FIG. 3, in the structure that lightsare returned respectively to a plurality of light receiving parts of thephotodetector 102 b having the optical path lengths from the signalrecording surface of the optical disc different from each other, onelens 110 is used as a lens for respectively providing the light fluxesin the light receiving parts as focal points on the light receivingparts.

[0013] Since the optical distances to the light receiving parts from thelens 110 are precisely different from each other, the hybrid opticalelement does not obtain the focal points at the same time. However, afocus error signal, a tracking error signal, a reflection signal (RFsignal) based on the reflected light flux read from the optical disc orthe like may be obtained so as to be allowable in practice. A step forreducing and adjusting the number of optical parts is simplified asmentioned above, so that the compact and inexpensive hybrid opticalelement can be realized.

[0014] The wavelength of light emitted from a light source used for theoptical pick-up device is shortened as well as the versatility ofrecording media such as the optical disc.

[0015] For meeting the versatility of the recording media, there areproposed optical discs such as a ROM optical disc in which aninformation signal is formed on a disk substrate by a micro irregularpit pattern, a phase change optical disc having a phase change recordinglayer in which an information signal can be recorded and reproduced, amagneto-optical disc having a magneto-optical recording layer in whichan information signal can be recorded and reproduced, etc.

[0016] In the ROM optical disc and the phase change optical disc, thereare provided areas having different reflectance depending on theinformation signals recorded on the optical disc and the change of lightintensity due to the difference in reflectance of light fluxes reflectedfrom the areas is detected to read the information signals recordedthereon. The magneto-optical disc uses a magneto-optical Kerr effect inthe magneto-optical recording layer and reads the information signalsrecorded based on the difference in polarizing angle of the reflectedlights.

[0017] The optical pick-up devices used for reading the informationsignals from these optical discs are also requested to satisfyrespective systems so as to meet the optical discs having theabove-described versatile recording systems. In the optical pick-updevices, the structures of the hybrid optical elements to be used arerespectively different so as to meet the optical discs respectivelyhaving different recording systems.

[0018] For instance, the photodetector 102 b of the optical pick-updevice used for reading the information signals from the ROM opticaldisc on which the information signals are recorded by the pit patternmay be provided with, as shown in FIG. 4, one four-divided lightreceiving part 111 for detecting a focus error signal and an RF signaland two light receiving parts 112 and 113 for detecting a tracking errorsignal which are arranged at positions to sandwich the four-dividedlight receiving part 111 in between them. The structure of the opticalelement for making the light reflected from the optical disc incident onthese light receiving parts is also simple. As compared therewith, thephotodetector 102 b of the optical pick-up device employed for readingthe information signals recorded on the magneto-optical disc needs, asshown in FIG. 5, light receiving parts 114 and 115 for detecting lightintensity for each of different polarized states in addition to onefour-divided light receiving part 111 for detecting a focus error signaland an RF signal and two light receiving parts 112 and 113 for detectinga tracking error signal. That is, since a magneto-optical signal isfeeble, a differential detection needs to be carried out by using thetwo light receiving parts 114 and 115 on the photodetector 102 b. Asdescribed above, the number of the light receiving parts is increased sothat the structure of the optical element for making the light reflectedfrom the optical disc incident on these light receiving parts islikewise complicated. In other words, in order to make the lightreflected from the optical disc incident on these light receiving parts,the reflected light needs to be branched into three light fluxes and atleast two prisms are required. At this time, as for the change ofpolarizing direction due to the magneto-optical Kerr effect, polarizedwaves are divided into P-polarized waves and S-polarized waves relativeto the reflecting surfaces of the prisms. The S-polarized wave isreflected on the reflecting surface of one prism to allow it to beincident on one light receiving part 114 of the photodetector 102 b andthe P-polarized wave is reflected on the reflecting surface of the otherprism to allow it to be incident on the other light receiving part 115of the photodetector 102 b. Thus, the change of the polarizing directioncan be detected. As for the reflected light when there is no informationsignal recorded on the optical disc, the arrangement of the hybridoptical element needs to be determined so that the intensity of theS-polarized wave is equal to that of the P-polarized wave or the opticalelements such as a ½ wavelength plate need to be used. As describedabove, to meet the various kinds of optical discs having differentrecording systems, the structure of the hybrid optical element havingthe optical pick-up device is complicated.

[0019] On the other hand, in order to meet the short wavelength of lightemitted from the light source, the index of refraction and the angle ofdiffraction of the optical elements forming the optical pick-up devicecause problems. For instance, for the optical pick-up device used forreading the information signals of the optical disc such as a CD onwhich the information signals are recorded by the pit pattern or themagneto-optical disc such as an MD, a light source for emitting lightwhose wavelength is 780 nm is employed. For the optical pick-up deviceused for a DVD, a light source for emitting light whose wavelength is650 nm is employed. Further, for the optical pick-up device used for theoptical disc capable of performing a high density recording, a lightsource for emitting light whose wavelength is 450 nm is employed.

[0020] When the index of refraction of the optical elements employed forthe optical pick-up device is examined, its imaginary part, that is, itsabsorption is firstly apprehended. In optical glass or a synthetic resinmaterial used as the material of the optical elements of the opticalpick-up device, light having the wavelength shorter than about 400 nm isgreatly absorbed. When such absorption arises, the output of emittedlight of the light source needs to be more increased in order to obtainnecessary reflected light. Further, since the change in quality of theoptical elements is generated, the degree of freedom in selecting thematerials of the optical elements is restricted. As the wavelength of alight flux becomes short, the angle of diffraction becomes small. Forinstance, assuming that the pitch of the diffraction grating is d, theangle of diffraction in this diffraction grating is represented asdescribed below.

sin=m/(nd)  (1)

[0021] (Here, m designates an integer, designates wavelength and ndesignates index of refraction.)

[0022] According to this formula (1), as the wavelength of the lightflux becomes short and becomes small, the angle of diffraction becomessmall under a condition that the pitch d and the index of refraction nare constant.

[0023] The plural light receiving parts formed on the PDIC need to beformed to have respective sizes and spaces so that photodetectionsignals corresponding to light fluxes respectively incident on the lightreceiving parts can be independently detected. Each size and space aredetermined depending on the property of the photodetector and acapability of a manufacturing step, and do not directly undergo alimitation of the wavelength of the light flux. That is, it may be saidthat the size and space of each light receiving part on thephotodetector are determined independently of the wavelength of lightemitted from the light source. Accordingly, the size and space in whicheach light receiving part can independently detect the photodetectionsignal may be considered not to depend on the wavelength of lightemitted from the light source and to be constant.

[0024] In this case, according to the above-described formula (1), anoptical distance to each light receiving part from the diffractiongrating needs to be lengthened in order to distribute the reflectedlight to and receive it by each light receiving part, so that thestructure may be possibly enlarged. In this case, as mentioned above,even when the focus positions of the reflected light are displaced fromthe position of the photodetector within an allowable range to make iteasy to form the hybrid optical element, the allowable range isextremely narrowed. In the present case, cannot be employed thestructure that the reflected light is converged on a plurality of lightreceiving parts by one lens as described above.

[0025] As described above, when the method for using the markers aspositioning marks to position the optical elements as mounting means isemployed, it is difficult to obtain a good positioning accuracy due to afact that the optical distance is long and an adequate positioningcannot be realized. When the optical distance to the light receivingpart from the diffraction grating increases twice for an angle settingaccuracy with the same accuracy, the positional displacement between thelight receiving part and a spot of light will becomes twice. Theabove-described positional displacement between the light receiving partand the spot of light causes the quality of the photodetection signalwhich is to be detected to be deteriorated. In the worst case, it isanticipated that the photodetection signal is not detected.

[0026] As mentioned above, in the hybrid optical element forming theoptical pick-up device, a signal detecting system is complicated withthe versatility of the optical discs as well as the improvement of therecording density, and further, a high accuracy in assembly is required.

[0027] For satisfying such a request, is carried out a double sidedmounting that the optical elements such as a lens, a prism, adiffraction optical element, etc. are attached to one surface of asubstrate serving as a base and a semiconductor laser serving as a lightsource and photodetectors are attached to the other surface of thesubstrate. Further, in an assembly step, while viewing the state of thephotodetection signal, a positioning (active alignment) is carried out.In order to realize the above-described structure and the assembly step,the substrate, the optical elements, the semiconductor laser and thephotodetector need to be formed in configurations adapted to suchstructure and assembly step. Firstly, as shown in FIG. 6, it isnecessary to form a light transmission hole 116 on a substrate 104 sothat the light receiving part 102 c of a photodetector 102 b can detectthe reflected light reflected by the optical disc through the lighttransmission hole 116. The photodetector 102 b needs to be attached tothe substrate 104 so as to oppose the light receiving part 102 c to thesubstrate 104.

[0028] An electric signal detected in accordance with the reflectedlight received by the photodetector 102 b needs to be taken outside thepackage of the hybrid optical element. As a first structure to this end,there is a structure that wiring is provided on a substrate 104 and aterminals of photodetectors are directly connected to the wiring.

[0029] As a second structure, for example, as described in JapanesePatent Application Laid-Open No. 2000-228534 and Japanese PatentApplication Laid-Open No. 2000-183368, there is a structure that a relaysubstrate through which electrodes are taken out is interposed betweenphotodetectors and a substrate. In the Japanese Patent ApplicationLaid-Open No. 2000-228534, there is disclosed a structure that thephotodetectors are connected to the relay substrate by an anisotropicconductive material. In the Japanese Patent Application Laid-Open No.2000-183368, there is disclosed a structure that optical elements areattached to one surface side of the relay substrate and thephotodetectors are attached to the other surface side by a flip chipbonding method.

[0030] As a third structure, are used photodetectors having a structurethat light receiving parts and electrode terminals are formed onopposite surfaces to each other.

[0031] However, the conventionally used photodetectors have structuresthat the light receiving parts and the electrode terminals are providedon the same surface and do not have structures that the light receivingpart and the electrode terminals are respectively arranged on both thesurfaces of one surface and the other surface.

[0032] The conventional hybrid optical element utilizes a structure thatwhen the photodetectors are sealed in package (PKG), the chips of thephotodetectors are mounted on a resin mold package and a wire bondingprocess is applied thereto to form a light receiving side with a moldedresin, or a structure that the chips of the photodetectors are mountedon a hollow package made of a molded resin or ceramics, a wire bondingprocess is applied thereto, and the package is covered with a flat platemade of a glass substrate or a synthetic resin.

[0033] As described above, the hybrid optical element and the PDIC(photodetector device) have the structure of the signal detecting systemcomplicated, need to have a high accuracy in assembly and not to carryout the conventional passive alignment, but to carry out the activealignment.

[0034] As the structures in which the active alignment can be carriedout, it may be said that the third structure is the simplest among thefirst to third structures. In the third structure, as shown in FIGS. 7Ato 7C, a photodetector 102 b is bonded to a substrate 104 by, forinstance, a UV (ultraviolet ray) curing resin so that the lightreceiving surface of the photodetector 102 b comes into contact with thesubstrate 104.and electrodes for taking out signals are formed on asurface opposite to the light receiving surface so that the signals canbe taken outside a package.

[0035] For manufacturing the photodetector having the above-describedstructure, there exist some technical problems to be solved. As one ofthe problems, there may be considered a formation of a lighttransmission hole. In the photodetector, the light transmission hole 116having the depth not less than the thickness of the substrate 104 needsto be provided. Accordingly, there may be considered problems such asthe relation between the opening area of the light transmission hole 116and the size of the photodetector 102 b, or an insulating part to beprovided on the inner peripheral surface of the light transmission hole116 and the disconnection and reliability of an electrode material to beinserted. Therefore, the photodetector having such a configuration ishardly formed.

[0036] The photodetector 102 b disposed on the substrate 104 is, asshown in FIG. 7C, electrically connected to the substrate 104 bywire-bonding between wire bonding pads 104 c provided on the substrate104 and wire bonding pads 102 d provided on the photodetector 102 b.

[0037] On the other hand, in the first structure, that is, the structurethat the photodetectors having the light receiving parts and theelectrode parts formed on the same surface are directly bonded to thesubstrate by a flip chip bonding process, it is difficult to carry outthe active alignment in which an assembly and a positional adjustmentare performed while viewing photodetection signals from thephotodetectors.

[0038] In order to output the photodetection signal from thephotodetector during a positioning operation while using the firststructure, for instance, a conductor such as a probe pin 117 needs to bebrought into contact with the electrode part of the photodetector 102 b.That is, when the active alignment is carried out in the first system, aspace into which the probe pin 117 is adequately inserted needs to beprovided between the photodetector 102 b and the substrate 104 while theposition of the photodetector 102 b is adjusted. Under a state that thesubstrate 104 is kept coming into contact with the photodetector 102 b,the position of the photodetector 102 b cannot be adjusted. When thespace is provided between the photodetector 102 b and the substrate 104during adjusting the position of the photodetector 102 b, a spot size onthe light receiving surface upon adjustment of the position is differentfrom a spot size after the assembly. Therefore, an output signal whichis precisely obtained upon adjustment changes after the assembly so thata precise positional adjustment is difficult.

[0039] It is extremely difficult to employ the first to third structuresfor the hybrid optical element in which at least one of optical elementsa lens, a prism, a diffraction element, etc., a light emitting element,and photodetectors are mounted on both the surfaces of the substratefrom the viewpoints as mentioned above.

[0040] When the photodetectors are sealed in a package (PKG), when alight source such as a violet blue laser which emits light whosewavelength is short, for example, about 400 nm is used, most of moldedresins absorb the light located in this wavelength band, so that asynthetic resin material which has been hitherto employed for infraredrays or visible lights (red to blue) cannot be used.

[0041] That is, in the structure that the chips of the photodetectorsare mounted on the resin mold package and the wire bonding process isapplied thereto to form the light receiving side by the molded resin,the molded resin having a high transmission factor in a short wavelengthband needs to be used, however, when a moldability and sealingcharacteristics or the like are taken into consideration, there is noproper material. In the structure that the chips of the photodetectorsare mounted on the hollow package made of the molded resin or ceramics,the wire bonding process is applied thereto, and then, they are coveredwith the flat plate made of the glass substrate or the synthetic resinor the like, not only a manufacture cost becomes high, but also anentire size is enlarged.

DISCLOSURE OF THE INVENTION

[0042] It is an object of the present invention to provide a new hybridoptical element and a photodetector device in which the above-describedproblems of the prior art can be eliminated.

[0043] It is another object of the present invention to provide a hybridoptical element and a photodetector device in which a compact and lightstructure is realized and the positions of photodetectors are easily andhighly accurately adjusted.

[0044] A hybrid optical element according to the present inventioncomprises a substrate; at least one optical element attached to onesurface of the substrate; a light emitting element and a photodetectorattached to the other surface of the substrate; and an intermediatemember interposed between the substrate and the photodetector. A basematerial constituting the intermediate member is formed with a materialhaving an absorption property in the wavelength of light emitted fromthe light emitting element. The intermediate member has a hole partthrough which a light flux incident on the photodetector is allowed topass and a part with a conductivity. The terminal of the photodetectoris connected to a conductor pattern on the substrate by the part withthe conductivity. The intermediate member functions as a relay substratefor connecting the terminal of the photodetector to the conductorpattern on the substrate.

[0045] Another hybrid optical element according to the present inventioncomprises a substrate; at least one optical element attached to onesurface of the substrate; a light emitting element and a photodetectorattached to the other surface of the substrate; and an intermediatemember interposed between the substrate and the photodetector. Theintermediate member is composed of a material having no absorptionproperty in the wavelength of light emitted from the light emittingelement, that is, a transparent base material having transmissioncharacteristics and has a part with a conductivity by which the terminalof the photodetector is connected to a conductor pattern on thesubstrate.

[0046] A photodetector device according to the present inventioncomprises a substrate; at least one optical element attached to onesurface of the substrate; a photodetector attached to the other surfaceof the substrate; and an intermediate member interposed between thesubstrate and the photodetector. The intermediate member is formed witha transparent material having no absorption property in the wavelengthof light emitted from a light emitting element, that is, a transparentbase material having transmission characteristics and has a part with aconductivity by which the terminal of the photodetector is connected toa conductor pattern on the substrate.

[0047] A hybrid optical element according to the present invention ismanufactured by attaching at least one optical element to one surface ofa substrate having a conductor pattern; attaching a light emittingelement to the other surface of the substrate; positioning aphotodetector to be attached to an intermediate member having a holepart through which a light flux incident on the photodetector is allowedto pass and a part with a conductivity and interposed between thesubstrate and the photodetector; then, attaching the intermediate memberto the other surface of the substrate; and further connecting theterminal of the photodetector to a conductor pattern on the substratethrough the part with the conductivity of the intermediate member.

[0048] Still another objects of the present invention and specificadvantages obtained by the present invention will become more apparentfrom the following description of embodiments made by referring to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049]FIG. 1 is a plan view showing assembly steps of a conventionalhybrid optical element.

[0050]FIG. 2 is a side view showing an optical pick-up device formed byusing the hybrid optical element.

[0051]FIG. 3 is a side view showing another example of the conventionalhybrid optical element.

[0052]FIG. 4 is a plan view showing a pattern of a light receiving partof a photodetector in the hybrid optical element.

[0053]FIG. 5 is a plan view showing other example of the pattern of thelight receiving part of the photodetector in the hybrid optical element.

[0054]FIG. 6 is a side view showing the structure of a main part of theconventional hybrid optical element.

[0055]FIG. 7A is a plan view showing the structure of the conventionalhybrid optical element, FIG. 7B is a side view thereof and FIG. 7C is abottom view thereof.

[0056]FIG. 8 is a side view showing an adjusting step of theconventional hybrid optical element.

[0057]FIG. 9 is a side view showing the structure of a hybrid opticalelement according to the present invention.

[0058]FIG. 10 is a plan view showing a relay substrate made of amaterial having no light transmission characteristics which forms thehybrid optical element.

[0059]FIG. 11 is a side view showing a state that wire ball bumps areformed on a photodetector by using a wire bonder in a manufacturing stepof the hybrid optical element.

[0060]FIG. 12 is a side view showing a state that the wire ball bumps onthe photodetector are shaped in the manufacturing step of the hybridoptical element.

[0061]FIG. 13 is a side view showing a state that the photodetector andthe relay substrate are positioned in the manufacturing step of thehybrid optical element.

[0062]FIG. 14 is a side view showing a main part under a state that thephotodetector is connected to the relay substrate through bumps in themanufacturing step of the hybrid optical element.

[0063]FIGS. 15A to 15F are perspective views and side views showing themanufacturing step of a photodetector unit when the relay substrate ofthe hybrid optical element is transparent.

[0064]FIG. 16 is a plan view showing the transparent relay substrateforming the hybrid optical element.

[0065]FIG. 17 is a side view showing the substrate to which a lightemitting element and optical elements are attached.

[0066]FIG. 18 is a side view showing the photodetector unit during themanufacturing step of the hybrid optical element.

[0067]FIG. 19 is a side view showing a state that the photodetector unitis positioned on the substrate in the manufacturing step of the hybridoptical element.

[0068]FIG. 20 is a side view showing the structure of a collet forholding the photodetector unit in the manufacturing step of the hybridoptical element.

[0069]FIG. 21 is a plan view showing a pattern of the light receivingpart of the photodetector forming the hybrid optical element.

[0070]FIG. 22 is a flow chart showing a manufacturing step of a relaysubstrate when a base material is ceramics.

[0071]FIG. 23 is a flow chart showing a manufacturing process of therelay substrate when a base material is a semiconductor.

[0072]FIG. 24 is a flow chart showing a manufacturing process of therelay substrate when a base material is a transparent material.

BEST MODE FOR CARRYING OUT THE INVENTION

[0073] Now, referring to the drawings, embodiments of the presentinvention will be described below.

[0074] A hybrid optical element and a photodetector device according tothe present invention comprises, as shown in FIG. 9, at least oneoptical element 2 including a lens, a prism and a diffraction elementattached to one surface side of a substrate 1, and a semiconductor laser3 as a light emitting element and a photodetector 4 attached to theother surface of the substrate 1. Between the substrate 1 and thephotodetector 4, a relay substrate 5 serving as an intermediate memberis interposed. A method for manufacturing the hybrid optical elementaccording to the present invention is a method for manufacturing such ahybrid optical element.

[0075] On the substrate 1, is formed a first through hole 8 for allowinga light flux outgoing from the semiconductor laser 3 to pass to the onesurface side of the substrate 1. On the substrate 1, is formed a secondthrough hole 9 for making light reflected from an optical disc incidentupon the photodetector 4 from the one surface side of the substrate 1 asdescribed below. As the semiconductor laser 3, is used a semiconductorlaser having the wavelength band of emitted light in the vicinity of 400nm or nearer to an ultraviolet radiation side than thereto.

[0076] The relay substrate 5 is formed of a material having anabsorption property in the wavelength of light emitted from thesemiconductor laser 3 as a base material. As materials having absorbingcharacteristics of the light of wavelength in the vicinity of 400 nm orthe light of wavelength nearer to the ultraviolet radiation side thanthereto, there can be used any of ceramic materials such as alumina,aluminum nitride or glass epoxy, or any of semiconductor materials suchas silicon, gallium-arsenic, indium-phosphorus or zinc selenide. On therelay substrate 5 formed by using the above-described materials, isformed a third through hole 6 for allowing the reflected light from theoptical disc to pass, as shown in FIG. 10.

[0077] The third through hole 6 provided on the relay substrate 5 isformed to have a size so as to allow at least the entire part of thephotodetector 4 to face the one surface side of the substrate 1.Further, when the third through hole 6 has such a size as to allowmarkers for positioning provided on the photodetector 4 arranged to besuperposed on the relay substrate 5 to face it, the assembling step canbe made easy and the structure of an assembling device can besimplified.

[0078] On the one surface of the relay substrate 5, wiring 7 is providedas a conductive part. In the wiring 7, nickel (Ni) as substrate metal iscoated with gold (Au). As materials forming the wiring 7, there may beused silver (Ag), tungsten (W), aluminum (Al), etc. as well as gold (Au)and nickel (Ni).

[0079] On the one surface of the relay substrate 5 having the wiring 7provided, are provided markers 7 a for positioning the arrangedpositions of the photodetector 4 to be arranged on the relay substrate5.

[0080] The photodetector 4 forming the hybrid optical element and thephotodetector device according to the present invention is previouslyattached to the relay substrate 5.

[0081] In order to attach the photodetector 4 to the relay substrate 5,as firstly shown in FIG. 11, wire ball bumps 10 of gold (Au) are formedon electrode terminals made of, for instance, aluminum (Al) formed inthe photodetector 4 under ultrasonic wave applied from a ultrasonic horn207 by employing, for instance, a wire bonder 201. Gold is supplied tothe photodetector 4 as a gold wire (Au wire) 202. At this time, thephotodetector 4 is mounted on a stage 203 with a temperature adjuster toheat the entire part of the photodetector 4 to 100° C. or higher so thatthe wire ball bumps 10 are effectively formed.

[0082] Then, as shown in FIG. 12, to make the height of the respectivewire ball bumps 10 uniform, the photodetector 4 is mounted on a pressingbase 204 to perform a pressing process by using a flat press plate 205with good flatness. At this time, the amount of fall of the press plate205 to the photodetector 4 is regulated by a spacer 206 mounted on thepressing base 204.

[0083] Subsequently, as shown in FIG. 13, the photodetector 4 on whichthe wire ball bumps 10 are formed is bonded to the relay substrate 5.This bonding, that is, a bump bonding is carried out in such a mannerthat the photodetector 4 is held by the ultrasonic horn 207 through anadsorbing collet 208 and the photodetector 4 is pressed to the relaysubstrate 5 mounted on the stage 203 with the temperature adjusterheated to about 100° C. to undergo a ultrasonic vibration.

[0084] At this time, the markers for positioning are formed on the relaysubstrate 5 and the photodetector 4 to position them in accordance withthe markers. The positioning operation is carried out in such a way thatthe markers of the relay substrate 5 and the markers of thephotodetector 4 are observed at the same time by a CCD camera 212through a positioning prism 209 and a prism 210 arranged between therelay substrate 5 and the photodetector 4 opposed to each other. Thepositioning prism 209 has an oblique surface directed to the relaysubstrate 5 and an oblique surface directed to the photodetector 4 toallow light from the relay substrate 5 and light from the photodetector4 to reach the CCD camera 212 at the same time.

[0085] In this bonding process, the wire ball bumps 10 of thephotodetector 4 need to assuredly come into contact with the wiring 7 onthe relay substrate 5. In order to allow the wire ball bumps 10 toassuredly come into contact with the wiring 7, for instance, as shown inFIG. 14, the width W₁ of the wiring 7 of the relay substrate 5 may beset to 100 m and the diameter R₁ of the wire ball bump 10 may be set to60 m. When the width W₁ of the wiring 7 is larger than the diameter R₁of the wire ball bump 10, as described above, a positioning step iseasily carried out. That is, when the pitch P₁ of the wire ball bumps 10is equal to the pitch P₂ of the wiring 7, the difference between thewidth W₁ of the wiring 7 and the diameter R₁ of the wire ball bump 10designates the width W₂ of positional displacement upon bonding.

[0086] After the positioning process, as shown in FIG. 13, theultrasonic wave is applied to the photodetector 4 from its back surfacethrough the adsorbing collet 208 connected to the ultrasonic horn 207.The wire ball bumps 10 are electrically and mechanically connected tothe wiring 7 through ultrasonic eutectic by the ultrasonic wave.

[0087] In the bonding process, a small amount of ultraviolet (UV) curingresin is supplied to the four corner parts of the photodetector 4 andthe relay substrate 5 and cured so that the photodetector 4 is bonded tothe relay substrate 5 with a stronger bonding strength. In this case,the ultraviolet curing resin needs to be supplied so as not to reach thelight receiving part of the photodetector 4.

[0088] When the photodetector 4 is bonded to the relay substrate 5, ananisotropic conductive material is, preferably, not employed. Theanisotropic conductive materials include a liquid type material or afilm type material. The liquid type material is ordinarily low in itsthixotropy and expected to spread over the entire part of thephotodetector 4. That is, there is a possibility that the anisotropicconductive material reaches the light receiving part of thephotodetector 4. Some of the anisotropic conductive materials havedifferent indexes of refraction from those of vacuum and absorb light.When the anisotropic conductive material reaches the light receivingpart of the photodetector 4, the strength the photodetection signal inthe photodetector 4 is weakened due to the absorption of light of theanisotropic conductive material. Since the index of refraction of theanisotropic conductive material is different from that of the vacuum, anoptical distance is modulated. In this case, the a film thickness of theanisotropic conductive material reaching the light receiving part of thephotodetector 4 needs to be controlled. However, such a control isdifficult, so that the anisotropic conductive material is preferably notused.

[0089] When the relay substrate 5 is formed with a material having noabsorption property relative to the light of wavelength emitted from thesemiconductor laser 3, that is, a transparent material having a propertyof transmitting the light emitted from the semiconductor laser 3, as abase material, the above-described through hole does not need to beprovided as shown in FIG. 15A. In this case, an antireflection coat (ARcoat) layer is desirably provided on respective surfaces 5 a and 5 b orone of them of the relay substrate 5 in accordance with the wavelengthof emitted light outgoing from the semiconductor laser 3. As thematerials having no absorption property relative to the light ofwavelength emitted from the semiconductor laser 3, may be used any ofsapphire, optical glass, a synthetic resin material, a group III nitridesemiconductor, zinc oxide and silicon oxide.

[0090] On the transparent relay substrate 5, as shown in FIG. 16, wiring7 including electrode parts 17 a for bumps are formed likewise theabove-described relay substrate 5. The wiring 7 is formed in such amanner that the electrode parts 17 a for bumps which are connected tothe photodetector 4 through bumps as mentioned above are electricallyconnected to terminal parts 17 b to be connected to external parts.

[0091] Also in this case, the photodetector 4 shown in FIG. 15B isbonded to the relay substrate 5 through bumps likewise theabove-described relay substrate 5. On one surface side of thephotodetector 4, a light receiving part 4 a is formed. On a peripheraledge part, are provided many connecting electrodes 4 b provided withwire ball bumps 10 are provided.

[0092] The relay substrate 5 is butted on the photodetector 4, as shownin FIG. 15C, in such a manner that the surface of the relay substrate 5on which the wiring 7 is provided is opposed to a surface of thephotodetector 4 on which the electrodes 4 b provided with the wire ballbumps 10 are formed. The relay substrate 5 and the photodetector 4butted as shown in FIG. 15C are pressed from both surface sides as shownin FIG. 15D, so that the electrodes 4 b of the photodetector 4 areelectrically and mechanically connected to the electrode parts 17 a forbumps of the relay substrate 5 through the wire ball bumps 10.

[0093] In the relay substrate 5 and the photodetector 4 bonded to eachother, the peripheries of the bonded parts are covered with a sealingmaterial such as an adhesive or low-melting glass 12 to seal inside thebonded parts, as shown in FIGS. 15E and 15F. The outer surface of thephotodetector 4 may be covered with a synthetic resin or tape or thelike to protect it.

[0094] The photodetector 4 is mounted on the relay substrate 5 and thebonded parts of them are sealed with the sealing material such as thelow-melting glass 12 or the like as described above to form aphotodetector unit 11 as shown in FIG. 15F.

[0095] Then, as shown in FIG. 18, the photodetector unit 11 in which thephotodetector 4 is formed integrally with the relay substrate 5 isattached to the substrate 1 to which the optical element 2 and thesemiconductor laser 3 are attached, as shown in FIG. 17. The opticalelement 2 and the semiconductor laser 3 are attached to the substrate 1by a bonding process. The optical element and the semiconductor lasermay be, what is called, temporarily bonded to the substrate 1 so thatthey can be detached in a post-step. As the adhesives to be used, theremay be exemplified, for instance, silver (Ag) paste, thermosettingresin, ultraviolet (UV) curing resin, etc. To suppress a thermaldeformation upon bonding, a low temperature curing resin or theultraviolet curing resin is desirably employed.

[0096] After the photodetector unit 11 is positioned to the substrate 1to which the optical element 2 and the semiconductor laser 3 areattached, the photodetector unit 11 is attached to the substrate 1. Asfor positioning, while the passive alignment that the positioningoperation is performed by using markers may be utilized, is desirablyused to improve a positional accuracy the active alignment that light isemitted from the semiconductor laser 3 and the positioning operation isperformed while viewing an output signal from the photodetector unit 11.

[0097] When the active alignment is carried out, as shown in FIG. 19,light is emitted from the semiconductor laser 3, a light flux L₁outgoing from the semiconductor laser 3 is reflected by using a dummydisc 220 and returned to the photodetector unit 11 as a reflected lightflux L₂. At this time, the photodetector unit 11 is supported by acollet 219 to locate the relay substrate 5 at a position where the relaysubstrate 5 comes into contact with the substrate 1. The positionaladjustment of the photodetector unit 11 in three directions includingdirections X, Y and Z which mutually intersect perpendicularly iscarried out in such a way that the photodetector unit 11 is moved bymonitoring an output signal from the photodetector unit 11 while thephotodetector unit 11 comes into contact with the substrate 1. Since thephotodetector unit 11 always comes into contact with the substrate 1,the optical path to the light receiving surface of the photodetector 4from the dummy disc 220 is always maintained to be constant.

[0098] The collet 219 for supporting the photodetector unit 11 supports,as shown in FIG. 20, the periphery of the relay substrate 5 and has aprobe 211 for taking out the output signal from the photodetector 4.

[0099] In this adjustment, signals to be monitored are differentdepending on the arrangement of the light receiving part in thephotodetector 4. For instance, the light receiving part of thephotodetector 4 detects a focus error signal in accordance with anastigmatic difference method by light receiving parts A, B, C and D forreceiving light in such a way that the light incident on the dummy disc220, reflected by the dummy disc 220 and then reflected light is dividedinto four parts. In light receiving parts E, I and F and light receivingparts G, J and H for receiving the reflected light respectively dividedinto three in parallel at both the sides of the light receiving parts A,B, C and D, a tracking error signal is detected by a push-pull method.Further, in the light receiving parts for detecting an RF signal byperforming a differential detection by two remaining light receivingparts K and L, the positional adjustment of the photodetector unit 11can be carried out on the basis of the following calculation resultsusing the outputs of light detected respectively from the lightreceiving parts. That is, as for a direction X along a recording trackon a recording medium in FIG. 21, the following calculation is used.

(A+D)−(B+C)

[0100] As for a direction Y perpendicularly intersecting the recordingtrack of the recording medium in FIG. 21, the following calculation isused.

(A+B)−(D+C) or (E+G)−(F+H)

[0101] A direction Z in FIG. 21 as the direction of an optical axis ofthe light flux outgoing from the semiconductor laser 3 can be adjustedby moving the semiconductor laser 3 in the direction of optical axis orproviding a spacer having a through hole between the photodetector unit11 and the substrate 1. When a prism which polarizes the light fluxoutgoing from the semiconductor laser 3 by 90° to make it incident onthe substrate 1 is attached to the substrate 1, the direction Z in FIG.21 can be adjusted by moving the semiconductor laser 3 along the mainsurface of the substrate 1.

[0102] As patterns of the light receiving part of the photodetector 4forming the hybrid optical element, various kinds of patterns areemployed. In the active alignment, a calculation for obtaining a signalto be monitored is properly determined depending on the pattern of thelight receiving part.

[0103] Now, steps for manufacturing the relay substrate 5 will bedescribed.

[0104] In order to manufacture the relay substrate 5, when the basematerial of which the relay substrate 5 is made is a ceramic materialincluding any of alumina, aluminum nitride or glass epoxy, since thesematerials do not transmit the light of a visible radiation band, holesare firstly opened on a material having a plurality of relay substrates5 connected and grooves are formed thereon to separate the material intoindividual relay substrates 5 in step st1, as shown in FIG. 22. Then, instep st2, aluminum or nickel forming the substrate layer of the wiring 7is formed by printing. In step st3, this substrate layer is sintered. Innext step st4, an upper wiring material such as gold is formed on thesubstrate layer of the wiring 7 by a plating method. In step st5, thematerial is separated into the individual relay substrates 5. Theceramic material employed here is advantageously inexpensive and high inits strength even when a thickness is decreased.

[0105] When the material forming the relay substrate 5, that is, thebase material is a semiconductor material including any of silicon (Si),gallium-arsenic (GaAs), indium-phosphorus (InP) or zinc selenide (ZnSe),the wiring 7 is formed by, what is called a dry etching method, as shownin FIG. 23. Since any of these semiconductor materials is a material tobe used in an ordinary semiconductor manufacturing process, the use ofthis material is advantageous from the viewpoint that a working processis established. That is, in step still, a perforating mask is formed. Instep st12, a wafer in which a plurality of relay substrates 5 areconnected together is perforated by a dry etching method. Then, in stepst13 to step st15, a wiring pattern and markers are printed, depositedand lifted off to form the wiring 7 and the markers 7 a. In step st16,the wafer is separated into the individual relay substrates 5 by cuttingwith a dicer.

[0106] Since the semiconductor material used here has a cleavageproperty, a plurality of relay substrates are easily formed on the waferand then they are readily separated into the individual relay substrates5. This step may be a general dicer step or a cleavage step in whichflaws are provided and broken. A step of photolithography using asemiconductor material has been already established in a semiconductormanufacturing process. Thus, the line width, the pitch and the thicknessof the wiring 7 can be highly accurately controlled. When the sizeaccuracy of the wiring 7 and the size accuracy of the relay substrate 5are low, that is, tolerance is large, a margin corresponding to thetolerance needs to be taken likewise in the substrate 1, andaccordingly, the substrate 1 is enlarged. When the substrate 1 isenlarged, all the size of the hybrid optical element is also enlarged.Therefore, when the size accuracy of the wiring 7 and the size accuracyof the relay substrate 5 are high, the substrate 1 can be made compactand the entire body of the hybrid optical element can be made compact.

[0107] Since the semiconductor material used for the relay substrate 5constituting the present invention does not absorb the light of a bandgap or lower, when the wavelength of light emitted from thesemiconductor laser 3 as a light source is located in the band gap orlower, the through hole 6 does not need to be provided on the relaysubstrate 5.

[0108] Further, also when the base material as a material forming therelay substrate 5 is any of materials including sapphire, optical glass,a synthetic resin material, a group III nitride semiconductor, zincoxide and silicon oxide, and which does not absorb the light located ina wavelength band and emitted from the semiconductor laser 3, thethrough hole 6 does not need to be provided on the relay substrate 5. Inthis case, to manufacture the relay substrate 5, in step st21 to stepst23 shown in FIG. 24, respective steps that a wiring pattern andmarkers are printed, deposited and lifted off are carried out on a waferin which a plurality of relay substrates 5 are continued to form thewiring 7 and the markers. In the step st24, the wafer is separated intothe individual relay substrates 5 by cutting with a dicer.

[0109] In the above-described respective examples, although the wireball bumps 10 are formed for each photodetector 4, the wire ball bumps10 may be formed on the wafer in which a plurality of photodetectors 4are continued. Similarly, in each example, although an individualphotodetector 4 is bonded to an individual relay substrate 5, they maybe bonded to each other under a state that both the photodetectors 4 andthe relay substrates 5 are formed on the wafers or either of them areformed on the wafer. The photodetectors may be preferably bonded to therelay substrates in the forms of wafers in view of productivity.

[0110] In the above-described examples, although the wire ball bumps 10are formed on the photodetector 4 and the wiring 7 is formed on therelay substrate 5, the wiring 7 may be formed on the photodetector 4 andthe wire ball bumps 10 may be formed on the relay substrate 5.

[0111] Further, in the above-described examples, although thesemiconductor laser 3 is employed as a light source, the kind of thelight source may not be limited to the semiconductor laser, and, forinstance, a light emitting element using an organic material or the likemay be employed.

INDUSTRIAL APPLICABILITY

[0112] As mentioned above, since the hybrid optical element or thephotodetector device according to the present invention includes asubstrate; at least one optical element attached to one surface of thesubstrate; a light emitting element and a photodetector or aphotodetector attached to the other surface of the substrate; and anintermediate member interposed between the substrate and thephotodetector. The intermediate member has a hole through which a lightflux incident on the photodetector is allowed to pass or is made of atransparent base material having no absorption property for light ofwavelength emitted from the light emitting element and has a part with aconductivity by which the terminal of the photodetector is connected toa conductor pattern on the substrate. Accordingly, an active alignmentthat a positioning operation is carried out while the photodetectionsignal outputted from the photodetector is monitored can be easilyperformed to improve the mounting accuracy of the photodetector. Theimprovement of the mounting accuracy of the photodetector makes itpossible to improve an accuracy meeting the short wavelength of thelight source and easily meet the optical pick-up device using acomplicated signal detection.

[0113] Since a conventionally utilized existing equipment can be used tomanufacture the hybrid optical element and the photodetector deviceaccording to the present invention, they can be manufactured withoutincreasing a manufacture cost.

1. A hybrid optical element comprising: a substrate; at least oneoptical element attached to one surface of the substrate; a lightemitting element and a photodetector attached to the other surface ofthe substrate; and an intermediate member interposed between thesubstrate and the photodetector; wherein the intermediate member isformed with a material having an absorption property in the wavelengthof light emitted from the light emitting element and has a hole throughwhich a light flux incident on the photodetector is allowed to pass, anda part with a conductivity by which a terminal of the photodetector isconnected to a conductor pattern on the substrate.
 2. The hybrid opticalelement according to claim 1, wherein the intermediate member iscomposed of any one of materials such as alumina, aluminum nitride orglass epoxy.
 3. The hybrid optical element according to claim 1, whereinthe intermediate material is composed of any of materials such assilicon, gallium-arsenic, indium-phosphorus or zinc selenide.
 4. Thehybrid optical element according to claim 1, wherein the intermediatemember is provided with electrode pads connected to the part with theconductivity, the photodetector is provided with electrode padsconnected to terminals and the electrode pads of the intermediate memberare bonded to the electrode pads of the photodetector by a flip chipbonding process under a state that a light receiving surface of thephotodetector is directed toward the intermediate member.
 5. A hybridoptical element comprising: a substrate; at least one optical elementattached to one surface of the substrate; a light emitting element and aphotodetector attached to the other surface of the substrate; and anintermediate member interposed between the substrate and thephotodetector; wherein the intermediate member is formed with atransparent material having no absorption property in the wavelength oflight emitted from the light emitting element and has a part with aconductivity by which a terminal of the photodetector is connected to aconductor pattern on the substrate.
 6. The hybrid optical elementaccording to claim 5, wherein the intermediate member is composed of anyone of materials such as sapphire, optical glass, a synthetic resinmaterial, a group III nitride semiconductor, zinc oxide, and SiC.
 7. Thehybrid optical element according to claim 5, wherein an AR coat filmwhich does not reflect the light of wavelength emitted from the lightemitting element is formed at least one surface of the intermediatemember.
 8. The hybrid optical element according to claim 5, wherein theintermediate member is provided with electrode pads connected to thepart having the conductivity, the photodetector is provided withelectrode pads connected to terminals and the electrode pads of theintermediate member are bonded to the electrode pads of thephotodetector by a flip chip bonding process under a state that a lightreceiving surface of the photodetector is directed toward theintermediate member.
 9. The hybrid optical element according to claim 5,wherein a part between the intermediate member and the photodetector issealed by a sealing material.
 10. A photodetector device a substrate; atleast one optical element attached to one surface of the substrate; alight emitting element and a photodetector attached to the other surfaceof the substrate; and an intermediate member interposed between thesubstrate and the photodetector; wherein the intermediate member isformed with a transparent material having no absorption property in thewavelength of light emitted from the light emitting element and has apart with a conductivity by which a terminal of the photodetector isconnected to a conductor pattern on the substrate.
 11. A method formanufacturing a hybrid optical element comprising the steps of:attaching at least one optical element on one surface of a substratehaving a conductor pattern; attaching a light emitting element to theother surface of the substrate; positioning and attaching aphotodetector to an intermediate member having a hole through which alight flux incident on the photodetector is allowed to pass and a partwith a conductivity and interposed between the substrate and thephotodetector; then, attaching the intermediate member to the othersurface of the substrate; and connecting a terminal of the photodetectorto a conductor pattern on the substrate through the part with theconductivity of the intermediate member.
 12. The method formanufacturing a hybrid optical element according to claim 11, whereinthe optical element is positioned and attached to the substrate by usingas a reference a through hole formed on the substrate for allowing thelight flux emitted from the light emitting element to pass.